The present invention relates to a magneto-optical recording and reproducing system useful in increasing a recording density of data to be recorded on a magneto-optical disk.
FIG. 5A illustrates magneto-optical recording by a magnetic field modulation system. As shown in FIG. 5A, a laser pulse output from an optical head 10 is irradiated onto a recording surface of a magneto-optical disk 11, and at the same time, an external field, modulated by recording data, is applied to the magneto-optical disk 11 by a magnetic head 12. When a temperature at a part irradiated by the laser pulse reaches a Curie temperature, the recording data is left in an orientation of the applied magnetic field.
Referring to FIG. 5B, when a part of a recording layer irradiated by the laser pulse reaches a Curie temperature, this part, corresponding to a spot size of the laser beam at the Curie temperature is magnetized by the external magnetic field, recording pits are formed along a recording track on the magneto-optical disk.
To increase a recording density in such a magnetic field modulation system, a pulse spacing T for driving a laser light source is made smaller than the spot size of the laser beam to partially overlap the recording pit previously formed and the recording pit subsequently formed, thus overwriting the subsequent recording pit at such an overlapped portion in a circumferential direction of the disk.
That is, while the pits are formed one by one in a time series manner, an intended increase in recording density causes the generation of the overlapped portion between the adjacent pits as shown in FIG. 5B, and the overlapped portion has information at a magnetization change point (edge), i.e., so-called edge recording is effected.
However, a pitch of the edge recording tracks is usually set to be equal to or larger than the laser spot diameter (about 1.5 .mu.m) which is limited by a wavelength .lambda. of the laser beam and a numerical aperture NA of an objective lens. Therefore, a recording density of data to be recorded in a radial direction of one optical disk is limited by the wavelength .lambda. of the laser beam.
While the data recording density in the radial direction of the optical disk becomes larger in inverse proportion to the pitch P of the recording tracks and the wavelength .lambda. of the laser beam, a reduction in the wavelength .lambda. and the track pitch P is considered to rely upon development of a new device, which has been difficult to realize.